So-called workstations for computer terminal work are in general embraced by the description below but in particular medical applications with the purpose of making diagnoses based on anatomical images of focused objects.
The diagnostic examination work of patient images from X-ray, MR (magnetic resonance imaging scanner) and ultrasound examinations requires great concentration and is more or less trying depending on prevailing circumstances regarding illumination and ergonomic functions with regard to strain and load.
A large disadvantage upon analogous examination of X-ray film, which is transilluminated by a light field lying behind, has always been disturbing stray light outside the limits of the film, which is both tiring and makes the diagnosis of examined objects more difficult. It is true that this can be remedied by delimiting dimming curtains, which however require both concentration and time to manoeuvre and not the least depending on the occurring different film sizes.
Another disadvantage of the analogous technique is the risk of underexposed and overexposed images, i.e., light and dark films, respectively.
Upon change to digital examination by computerized display devices, the disturbing-light problem becomes negligible and too light or dark images are fixed by so-called image manipulation.
The difference in light intensity between analogous negatoscopes and display devices is about factor 10, but counted in light transmission, the difference is negligible and occasionally the opposite.
Therefore, it is not unusual that the user erroneously thinks that the sharpness and contrast of the details on the display device are improved by a weak surrounding illumination.
Too low a light intensity of the surrounding illumination in relation to the display device may have the opposite effect and become tiring by generating so-called melatomia, i.e., sleep requirement. Upon trying to focus on adjacent papers having text, also the reading is made more difficult due to erroneous luminance ratio.
The National Swedish Board of Health and Welfare is, for instance, of the opinion that good contrast for doing computer terminal work is at hand if the luminance ratios between adjacent surfaces in the working area, i.e., so-called infield, surround field and outer field of vision, should be of 5:3:1. The infield is within a radius of about 20 cm from the focus of the examiner, surround field within a radius of about 40-50 cm and outer field of vision beyond that.
In conclusion, the following primary physiological factors are valid for the function of the eye and working capacity-decreasing results: At a large pupil, the depth of field of the eye decreases, thereby increasing requirements on correct viewing distance.
Too weak light deteriorates the detail viewing in varying degree.
From this, anybody realizes that the combination mentioned above considerably increases the risk of imperfectly made diagnoses, such as, e.g., undiscovered tumours or other symptoms being life-threatening or serious to the patient.
The number of digital workstations varies with the size and extent of the examination unit. A smaller department comprises as a rule 4-8 workstations and a larger 20-30 workstations. Even if the workstations are distributed between various numbers of rooms, it is inevitable that a smaller or greater number of workstations are placed neighbouring each other for reasons of space or organisation. Thereby, upon image analysis and diagnostics, varying disturbances arise in concentration depending on the activity of the department and the amount of movable personnel and not the least incident light from windows, inappropriately placed general lighting, etc.
It is true that the imaging technique of the computerized digital workstations offers many technical and ergonomic advantages in order to facilitate image processing, analysis and diagnosis in comparison with analogous technique. Unfortunately, in other respects the equipment is not adapted to existing wishes and ergonomic requirements with regard to vision, strain and workload.
The shortcomings of the digital workstations in vision ergonomics are summarized according to the following:
Measures are lacking for facilitating the light adaptation and contrast viewing of the eye at different viewing conditions.
Screening off of the workstations from disturbing factors such as external illumination, incident glaring daylight via windows as well as activities from other personnel and equipment such as, e.g., other workstations, so-called large screen projectors, copying machines, automatic drink dispensers, etc., is inferior.